The presence of combustion fumes in housing is a significant and serious problem that can cause chronic illness and accidental death. It has been estimated that approximately 500 accidental deaths per year in the U.S. are attributable to improper venting of combustion fumes in housing. Combustion fumes can result from fuel fired appliances like furnaces, water heaters, gas ranges, gas dryers, portable heaters, wood stoves and fireplaces. Research on combustion spillage from combustion appliances has estimated that 30 to 80% of homes in heating climates have incidence of combustion fumes venting into the occupied spaces of houses. Combustion fumes can contain a variety of toxic and harmful gases including nitrous oxide, nitrogen dioxide, sulfur dioxide, carbon monoxide, hydrocarbons and respirable particulates. Carbon dioxide, oxygen and nitrogen are also the non-toxic and major constituent byproducts of the combustion exhaust.
Causes of combustion exhaust entrainment in homes include: malfunctioning equipment, cracked or broken flues and heat exchangers, improper installation, lack of maintenance, tight building construction and the creation of negative pressures in the home that can cause reversal of combustion fumes in chimneys and flues.
In response to this serious problem, there has been rapid growth in the sale of carbon monoxide alarms for home use. In 1997 there were approximately 5 million residential carbon monoxide detectors sold in the U.S.
There are a number of drawbacks to the use of current CO sensors in homes.
The first of these drawbacks is that since these products are only targeted to measure carbon monoxide they are only addressing one of many harmful byproducts of combustion. In fact, some byproducts like nitric oxide have the same physiological effect as carbon monoxide but at one third to one fifth the concentration level. Very low concentrations of other byproducts like nitrogen dioxide have been shown in numerous studies to increase the incidence of respiratory symptoms and illness in children. Carbon monoxide sensors do not provide complete protection from exposure to combustion fumes.
Another drawback of the currently used CO sensors is that residential carbon monoxide sensors have been very problematic in operation. There have been widespread reports of false alarms, susceptibility to alarm when exposed to common household chemicals and malfunctioning alarms. A recent evaluation of four major brands of commercially available residential CO sensors by the Gas Research Institute found that for some brands up to one out of three units will fail to alarm at UL specified concentrations.
Finally, most of the detectors available on the market today are not accurate for measuring concentrations below 60 ppm of carbon monoxide, which may be harmful to adults over prolonged exposure and may cause chronic health problems for children, the elderly and individuals with heart and respiratory problems.
Accordingly, there exists a compelling need for better methods of detecting improper venting of combustion appliances, especially within interior spaces such as homes. In addition, there is also a need for early detection of low levels of improper venting. By identifying low levels of leakage before they become larger, remedial steps can be taken before leakage becomes larger and potentially more dangerous, if not deadly.